About

Flavius Pop is an Assistant Research Professor in the Department of Electrical and Computer Engineering at Northeastern University College of Engineering. His research involves advanced topics in electrical and computer engineering, with a focus on microelectronics and photonic devices. He is engaged in collaborative research efforts, including partnerships such as the Singapore Research Attachment Program (SRAP), which provides immersive research opportunities for PhD students in areas like piezoelectric MEMS and ultra-high-speed photonic devices. His work contributes to the development of innovative microelectronic and photonic technologies, supporting the college's mission of research excellence and industry partnership.

Research topics

• Computer Science
• Acoustics
• Physics
• Telecommunications
• Electrical engineering
• Engineering
• Electronic engineering
• Algorithm
• Materials science
• Optics
• Optoelectronics

Selected publications

• Implantable Medical Devices Detection Based On Piezoelectric Micromachined Ultrasonic Transducers and A Micropython Internet of Medical Things Nodes

  2022 IEEE 35th International Conference on Micro Electro Mechanical Systems Conference (MEMS) · 2022-01-09 · 3 citations

  article1st authorCorresponding

  This paper demonstrates, for the first time, a detection system for Implantable Medical Devices (IMDs) based on Piezoelectric Micromachined Ultrasonic Transducers (PMUTs). The system is connected to a cloud service through a low-cost MicroPython microcontroller acting as an Internet of Medical Things (IoMT) node. A PMUT array, acting as an ultrasonic antenna and intrabody range-finding device, is used to detect the implantation distance of several IMDs through the Time-of-Flight (ToF) method. The collected measurements are then transmitted to the cloud over the microcontroller's WiFi board where the monitoring is done real-time upon the reception of each data-set. Ultimately, this work shows the detection of three IMDs implanted at several distances in a tissue phantom, the implementation of a TX and RX circuit, the design and fabrication of PMUTs, the detection protocol in MicroPython, and the real-time processing algorithm run on the cloud platform.

  PublisherDOI

• Lithium Niobate Piezoelectric Micromachined Ultrasonic Transducers for high data-rate intrabody communication

  Nature Communications · 2022 · 74 citations

  1st authorCorresponding
  • Computer Science
  • Materials science
  • Acoustics

  In recent years, there has been an increased interest in continuous monitoring of patients and their Implanted Medical Devices (IMDs) with different wireless technologies such as ultrasounds. This paper demonstrates a high data-rate intrabody communication link based on Lithium Niobate (LN) Piezoelectric Micromachined Ultrasonic Transducers (pMUTs). The properties of the LN allow to activate multiple flexural mode of vibration with only top electrodes. When operating in materials like the human tissue, these modes are merging and forming a large communication bandwidth. Such large bandwidth, up to 400 kHz, allows for a high-data rate communication link for IMDs. Here we demonstrate a full communication link in a tissue phantom with a fabricated LN pMUT array of 225 elements with an area of just 3 by 3 mm square, showing data-rates up to 800 kbits/s, starting from 3.5 cm and going up to 13.5 cm, which covers the vast majority of IMDs.

  PublisherOA PDFDOI

• Zero-Power Ultrasonic Wakeup Receiver Based on MEMS Switches for Implantable Medical Devices

  IEEE Transactions on Electron Devices · 2022 · 20 citations

  1st authorCorresponding
  • Computer Science
  • Electrical engineering
  • Computer Science

  This article demonstrates, for the first time, a zero-power ultrasonic wakeup receiver for intra-body communication with Implantable Medical Devices (IMDs). The system is based on a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${10} \times {10}$ </tex-math></inline-formula> Piezoelectric Micromachined Ultrasonic Transducer (pMUT) array, a zero-power 500 nm gap MEMS plasmonic switch, a low-leakage CMOS load-switch, and an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ad hoc</i> sensing circuit. An ultrasonic signal of 10 mVpp is received by the pMUT array at a distance of 5 cm and brings the MEMS switch from the OFF-state (1 pA) to the ON-state ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20~{\mu } \text{A}$ </tex-math></inline-formula> ) when biased at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9.09~{V}_{\text {DC}}$ </tex-math></inline-formula> . This small current then wakes up the load-switch (< 10 nW when off), which powers up the sensing circuit to decode the pMUT signal. The system is demonstrated in a tissue phantom, making it ideal for intrabody communication.

  PublisherDOI

• Intrabody communication for real-time monitoring of implanted medical devices based on piezoelectric micromachined ultrasonic transducers

  2021-01-01

  dissertation1st authorCorresponding

  Nowadays when we think about medical devices and patient monitoring, we can easily imagine ourselves laying down in a hospital bed, wires coming out of everywhere, and being looked after by nurses and physicians. Scary and not that comfortable. For this reason, medical wearable devices are becoming more popular for at-home monitoring and transmitting data back to the hospital. Sometimes wearables are not enough, this is why Implantable Medical Devices (IMD)s are still required to monitor many vital signs (blood flow, insulin level, neurons reading etc.) and act upon these readings (nerve stimulation, heart defibrillation, insulin pumping etc.). In order to be minimally invasive, reduce the risk of infection and rejection from the body, and last a long time (avoiding any further surgery) the IMDs require robust wireless communication technology to communicate with the external world. In this work I am going to show how we can implement an ultrasonic wireless communication link based on Piezoelectric Micromachined Ultrasonic Transducers (pMUT) arrays. pMUT arrays can be integrated with existing IMDs, used for wireless power charging, and can enable communication links for receiving and transmitting data. Moreover, I will show the modeling and design of the pMUT arrays, followed by the fabrication process and the device's characterization for system level validation. At this point, the communication link is implemented with arrays implanted in a tissue phantom and the channel is characterized at several distances. During the second part of this manuscript, I will show novel techniques to improve the ultrasonic communication link such as duplexing matching networks for bandwidth definition and direct modulation for implantation depth increase and direct bitstream feeding. In the future I envision that the number of IMDs are going to increase, and therefore I developed a scanning protocol that will allow medical doctors to find all implanted devices. This is the equivalent of an "ultrasonic stethoscope". Given the small form-factor of the IMDs these will have little to no space for a battery, limiting the operation lifetime. For this reason, I developed an Ultrasonic Wakeup Receiver (UWuRx) based and on the direct modulation system and on a Micro Electro-Mechanical System (MEMS) switch which allows for near zero-power consumption in the idle state. This UWuRx enabled on-demand device usability and limited the idle power consumption, which leads to battery life extension. Finally, I will show the development of a novel class of pMUTs based on thin-film X-cut Lithium Niobate (LN) piezoelectric layer to increase the transmission bandwidth and increase the communication data-rate of an arbitrary communication scheme.--Author's abstract

  PublisherDOI

• Implantable Bio-Heating System Based on Piezoelectric Micromachined Ultrasonic Transducers

  2020-01-01 · 5 citations

  article1st authorCorresponding

  This paper demonstrates, for the first time, on the possibility to achieve implantable bio-heating systems based on Piezoelectric Micromachined Ultrasonic Transducers (pMUTs). Given the miniaturization capability and bio-compatibly of the pMUTs, this will enable non-invasive implantable platforms for ultrasonic therapies. By implanting the arrays in key locations into the body or integrating them into smart ingestible pills, it will be possible to pre-monitor ailment manifestation, continuously and non-invasively apply the ultrasound therapy, and ultimately post-monitor the effects on the individual. This first demonstration has shown a 4°C increase in relative temperature in less than ten seconds with a five by ten pMUT array. In an implanted system, this will allow to locally heat tissue areas from 37°C to 41°C, making it ideal for hyperthermia therapies.

  PublisherDOI

• Miniaturized PMUT-Based Receiver for Underwater Acoustic Networking

  Journal of Microelectromechanical Systems · 2020 · 28 citations

  • Computer Science
  • Electronic engineering
  • Computer Science

  The present work reports on the novel implementation of a miniaturized receiver for underwater networking merging a Piezoelectric Micromachined Ultrasonic Transducer (PMUT) array and signal conditioning circuitry in a single, packaged device. Tests in both a large water tank and a pool demonstrated that the system can attain large enough Signal-to-Noise Ratio (SNR) for communication at distances beyond two meters. An actual communication test, implementing an Orthogonal Frequency Division Multiplexing (OFDM) scheme, was used to characterize the performance of the link in terms of Bit Error Rate (BER) vs SNR. In comparison to previous work demonstrating high-data rate communication for intra-body links and acoustic duplexing, this implementation allows for significantly larger distances of transmission, while addressing the signal conditioning and submersible packaging needs for underwater conditions, thus enabling PMUT arrays for operating as complete underwater communication receivers.

  PublisherDOI

• Dual Range and High Data-Rate Intrabody Communication Transceiver based on Piezoelectric Micromachined Ultrasonic Transducers

  2020-07-01 · 2 citations

  article1st authorCorresponding

  In this paper, we demonstrate the implementation of a dual range (short d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</sub> =3.5cm and long d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> =13.5cm distance application) and high bandwidth, high data-rate transceiver ( BW ≈ 200kHz and Data-Rate ≈ 400kbits/s) for intrabody communication links based on Piezoelectric Micromachined Ultrasonic Transducers (pMUTs). The transceiver consists of a Quadrature Phase-Shift Keying (QPSK) modulation and demodulation scheme implemented in a Universal Software Defined Radio (USRP). The intrabody antennas consist of a 10×10 uni-morph pMUT array based on Aluminum Nitride (AlN) with circular shape design and resonance frequency f ≈ 700kHz. The arrays are embedded in a tissue phantom to mimic human tissue properties and are coupled with ultrasound gel to avoid air gaps. The system was tested by serializing a 100×50pixels image in a bit stream and transmitting over the intrabody link. The sampling rate was set at twice the bandwidth of the pMUTs based on the Nyquist theorem. The detected Bit Error Rate (BER) was 1E-4 and 1E-1 for short and long range respectively, demonstrating the functionality of the pMUT intrabody transceiver. These levels of BER allow for perfect reconstruction of the original data by time-averaging successive frames.

  PublisherDOI

• Enabling Real-Time Monitoring of Intrabody Networks Through the Acoustic Discovery Architecture

  IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control · 2020-06-17 · 7 citations

  article1st authorCorresponding

  This article proposes the first acoustic discovery architecture (ADA) for intrabody networks (INs). The main objective of ADA is to discover and interrogate, in real-time (RT), all the implanted medical devices (IMDs) that are part of an IN. This permits noninvasive RT diagnosis for patients with multiple IMDs. ADA will allow medical doctors to have vital information, on-the-go, for treating patients and to constantly monitor them. The architecture was implemented in a network simulator emulating a real-life IN, based on preliminary experimental results. ADA is in charge of scanning the body volume, by exploiting the beam-forming and beam-steering capability of piezoelectric micromachined ultrasonic transducers (pMUTs) arrays, and efficiently interrogating all the reached devices for their status. As a result, a full IN map can be reconstructed together with all the vital signs of a patient. ADA shows very good RT capabilities, with a full scanning time from 1500 down to 100 ms and energy consumption from 2.6 down to 0.2 mJ, depending on the scanning accuracy, for a body torso volume of [Formula: see text].

  PublisherDOI

• Modeling and Optimization of Directly Modulated Piezoelectric Micromachined Ultrasonic Transducers

  Sensors · 2020-12-29 · 9 citations

  articleOpen access1st authorCorresponding

  The present work details a novel approach to increase the transmitting sensitivity of piezoelectric micromachined ultrasonic transducer arrays and performing the direct modulation of digital information on the same device. The direct modulation system can reach 3× higher signal-to-noise ratio level and 3× higher communication range (from 6.2 cm boosted to 18.6 cm) when compared to more traditional continuous wave drive at the same energy consumption levels. When compared for the same transmission performance, the direct modulation consumes 80% less energy compared to the continues wave. The increased performance is achieved with a switching circuit that allows to generate a short high-AC voltage on the ultrasonic array, by using an LC tank and a bipolar junction transistor, starting with a low-DC voltage, making it CMOS-compatible. Since the modulation signal can directly be formed by the transmitted bits (on/off keying encoding) this also serve as the modulation for the data itself, hence direct modulation. The working principle of the circuit is described, optimization is performed relative to several circuital parameters and a high-performance experimental application is demonstrated.

  PublisherOA PDFDOI

• An 18 nW −47/−40 dBm Sensitivity 3/100 kbps MEMS-Assisted CMOS Wake-Up Receiver

  IEEE Transactions on Circuits and Systems I Regular Papers · 2019-07-29 · 23 citations

  article

  This work demonstrates a low-power wake-up receiver utilizing a MEMS resonant device followed by CMOS demodulator and rectifying trigger circuits. The MEMS device is a Lamb wave piezoelectric-based acoustic resonator utilizing a thin film of lithium niobate (LN) which possess the largest reported electromechanical coupling factors (k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). This parameter, in conjunction with the high Q, is of paramount importance in providing for passive voltage amplification and filtering of the input signal. The CMOS demodulator is a 9-stage differential cross-coupled passive rectifier circuit designed with a differential output. It demodulates the signal from the MEMS resonator with the same gain as that could be achieved by a single-ended rectifier, but with half the charging time for double the single-ended bitrate. The rectifier's output is AC-coupled and fed to a two-stage differential voltage amplifier. Finally, an active latch rectifier is used to trigger a wake-up signal. The wake-up receiver is tested with an on-off keying modulated signal with carrier frequency around 400 MHz achieving a bit rate up to 100 kbps. This newly proposed system exhibits a sensitivity of -47 dBm at 3 kbps while consuming a total power of 18 nW.

  PublisherDOI

Frequent coauthors

• Matteo Rinaldi

  Scuola Normale Superiore

  31 shared

• Bernard Herrera

  Northeastern University

  28 shared

• Cristian Cassella

  Universidad del Noreste

  20 shared

• Gabriel Vidal-Álvarez

  Carnegie Mellon University

  5 shared

• Gianluca Piazza

  University of Cambridge

  5 shared

• Pierre Etienne Allain

  5 shared

• Abhay Kochhar

  5 shared

• Hideki Kawakatsu

  The University of Tokyo

  5 shared

Education

• PhD in Electrical and Computer Engineering

  Northeastern University

  2021

• Visiting Scholar

  Carnegie Mellon University

  2016

• MS in Electrical and Electronics Engineering

  Università degli Studi di Udine

  2016

• Visiting Scholar

  The University of Tokyo

  2015

• BS in Electrical and Electronics Engineering

  Università degli Studi di Udine

  2014